Locher



H. LOCHER WARP FEEDING March 17, 1964 3 Sheets-Sheet 1 Filed Nov. 6,1961 INVENTOR HANS Locum Kl H. LOCHER WARP FEEDING March 17, 1964 5Sheets-Sheet 3 Filed Nov. 6, 1961 INVENTOR H/ms LocneR By A34.

Anm.

United States Patent,

3,125,127 WARP FEEDING Hans Locher, Uster, Switzerland, assignor toZellweger Ltd., Uster Factories for Apparatus and Machines, Uster,Switzerland, a corporation of Switzerland Filed Nov. 6, 1961, Ser. No.150,280 5 Claims. (Cl. 139-97) The present invention relates toimprovements in warp let-offs on looms and, in particular, warp tensionand speed regulating means and is a continuation-inpart of myapplication Serial No. 847,988 filed October 22, 1959, under the titleMethod and device for electrically controlling the warp tension in loomsfor weaving, now Patent No. 3,072,154.

Warp let-offs are means for paying out warp at a rate suflicient to keepthe warp threads under tension while they are being woven. Warp let-olfsshould keep the warp tension constant when paying out the warp from thewarp beam and taking up the fabric on the cloth beam; they should payout the same warp length at every pick and they should compensate warptension fluctuations caused by the shedding shaft movements.

Keeping the warp tension constant is a factor of utmost importance inobtaining both satisfactory operation and uniformity of the fabric. If,when weaving, the warp is highly stressed, the risk of thread breakageis substantially increased and the loom efliciency is reduced byfrequent stoppages.

Many of the known let-off means have the disadvantage that they pay outonly the warp required for each pick but not the extra length neededtemporarily for each shedding operation most of which is payed back onshed closing. Conventional let-off means depend on the warp elasticityfor this purpose, with the result that the threads periodically areadditionally strained.

Resiliently mounted whip rolls have been proposed as a remedy, i.e.,means usually serving as a back rest, pressing against the warp threadsand capable of movement to maintain desirable tension notwithstandingthe fluctuations in warp tension produced by the shedding and beat-up.Such whip rolls have the disadvantage that, owing to the inertia of theoscillating masses, compensation occurs too late so that under certainconditions dynamic tension is produced in lieu of the desiredcompensation, whereby warp tension is actually increased instead ofbeing reduced. Looms are known, for example, which supply the extra warplength required for shedding by a whip roll drive whereby the roll isoscillated synchronously with the shedding operation and most of theotherwise occurring, periodic additional warp tension is avoided. Suchdrives, however, require additional mechanisms and in most cases they donot ensure full compensation during the entire weaving operation.

To provide uniform warp let-oif, various methods and devices are in use.Depending on the loom type and the material to be woven, positive ornegative let-oif motions are used. The negative let-off is based onfriction and has the disadvantage that the warp beam is forciblyoscillated by the warp so that the fluctuations in temporary dynamicwarp tension are substantially magnified. Brake means act on the warpbeam and are disengaged therefrom upon a rise of the warp strain beyonda predetermined value, whereby the warp beam may be turned through suchan angle that the warp strain drops for a period of one or more weavingcycles. In a positive let-ofi the warp beam is mechanically driven sothat the warp required is automatically supplied. To such end, stepwisedrives are provided, for example, turning the warp beam through acertain angle after each pick. Such positive let-off is not affiictedwith said disadvantage of the negative let-01f, but the decrease indiameter of the warp wound on the beam must be compensated bycomplicated arrangements.

Let-oif motions that maintain warp tension with the aid of mechanicalarrangements have the disadvantage that after a loom stoppage or a warpmanipulation during which the warp tension has been arbitrarily changed,a number of picks (under certain conditions ten or more) will berequired for bringing about a desired stable mean warp strain by meansof the mechanical warp tension control. As a result, the appearance ofthe piece of cloth woven in this period is decidedly different from thatof the remainder of the cloth, due to the dilferent spacing of the weftthreads. Such irregularities occur after each loom stoppage and impairthe cloth quality. Certain conventional let-offs form a closed controlloop in which a mechanical magnitude is measured and a signal producedthereby mechanically controls said magnitude. As such mechanical systemsdo not include amplifiers, the control either requires too much time oris inaccurate.

The general object of the invention is to overcome the disadvantages ofconventional systems for maintaining the warp tension in weaving.

A further object is a method of and apparatus for controlling themovement of the warp beam to maintain a substantially uniform warptension during weaving.

In its broadest aspect the invention comprises a method of and apparatusfor letting off the warp from the beam in such a manner as to satisfythe warp requirements of both each pick and each shedding operation.

An electrical signal corresponding to the tension of the warp betweenthe cloth and warp beams is continuously compared with a second signalcorresponding to the desired constant warp tension and the warp beam isdriven at a rate corresponding to the magnitude of the differencebetween the two signals to let off or take up warp according to thepolarity of the difference between the two signals.

According to an important feature of the invention, the warp beam isfurther varied in synchronism with the weaving cycle of the loom toanticipate and substantially compensate for the changes in tension ofthe warp produced by the opening and closing of the shed.

The apparatus of the invention comprises a device for producing a firstelectric signal U corresponding substantially to the instantaneous warptension P between the warp beam and the cloth beam, a voltage source forproducing a second electric signal U that corresponds to the set pointof the warp tension P, means for forming a third electric signal U thatcorresponds to the difference between the first two signals U and U anelectric amplifier for amplifying signal U to produce an amplifiedsignal U and an electromechanical motor operator actuated by signal Uand having a drive shaft which changes the direction of its rotationwhen the polarity of signal U changes, and which rotates at a speedcorresponding to the amplitude of signal U said drive shaft beingmechanically connected to the warp beam.

One form of the present invention and modifications of major partsthereof are shown, by way of example, in the drawings, wherein:

FIG. 1 diagrammatically shows the basic parts of a loom and a warplet-01f as disclosed by the invention.

FIG. 1a. is the wiring scheme for an amplifier input.

FIG. 2 illustrates an electric warp strain meter and its wiring layout.

FIG. 3 depicts the relation between armature strokes and potential inthe meter shown in FIG. 2. l

FIGS. 4 and 5 are diagrams showing the relation between input signal andoutput signal of two modifications of an amplifier forming part of themeans disclosed by the invention.

FIG. 6 schematically shows an electromechanical motor operator.

FIG. 7 is a diagram showing the movement of a shedding shaft and theconcurrent warp tension during a weaving cycle.

In FIG. 1 numeral 27 schematically shows the loorn frame in which ismounted a warp beam 1 carrying a warp 2. The latter is run over a whiproll and drawn,

in a manner known per se, through a harness of which are shown twoweaving shafts 18. The fabric made in the sheds 19, 19 is run around abreast beam 23 and wound upon. the cloth beam 26 via take-up rolls 24.The drive mechanism for the harness shafts 18, being irrelevant for thepresent invention, is not shown. The loom is operated by a motor 29 thatdrives the main shaft 20 and an eccentric shaft 14. Main shaft 20comprises crankarms which through connecting rods 21 reciprocate the lay22 with the reed' for beating up. Motor 29 is fed from the mains via amain switch 25. The speed of eccentric shaft 1,4 ishalf that of mainshaft 20. The loom further comprises known weft inserting means which,however, are not shown in the drawing as they are irrelevant for thepresent invention.

Warp beam 1 is rotated by a worm gearing comprising a worm 4 and a Wormwheel 3; worm 4 being fast on a shaft. 67 which is rotated in gearing10. The latter is driven by loom motor 29 by a pulley 13. Whip roll 5 at5 is rotatably mounted in crankarms 6 which are pivoted on axles 7, andis braced through springs 8 against a transverse bar 28 fixed to theloom frame. The force P exerted by warp 2 on whip roll 5, which force isa component of the total warp tension P, is taken up by the spring 8 sothat whip roll 5 occupies a position of equilibrium corresponding tothewarp tension. Fluctuations in the latter thus give rise to changes inthe position of roll 5, which changes are converted to variableelectrical quantities in a converter 9.

To such end, converter 9 comprises variable inductance means including acoil 42 and anarmature 41. The latter is joined to roll 5 by aconnecting member and thus follows the movements thereof. Thereby ischanged the gap between coil 42 and armature 41 in accordance with warptension component P. An alternating current IN flowing through coil 42thereby undergoes like changes so that the alternating potentialappearing on coil 42 illustrates electrically the warp tension P. Saidalternating potential is rectified in a rectifier 44 and smoothed by acapacitor 48. A direct voltage U is produced, of which the magnitudedepends on warp tension P or, respectively, one component P thereof, andwhich reproduces changes thereof in an inertialess manner.

A reference voltage U representing the magnitude of the warp strain thatactually has to be maintained, is tapped from a potential dividercomprising a potentiometer 38 and a resistor 38' and to which is applieda fixed direct voltage supplied by a source of potential 34. If the warptension has been correctly set, U is equal to U i.e., their difierenceis zero. Any deviation of the warp tension from said value gives rise toa positive or negative value of U Series resistor 38' is bridged by aswitch 35 that is open in normal operation. When main switch 25 isopened, i.e. when the loom is stopped, switch 35 shortcircuits seriesresistor 38. Thereby voltage U prevailing atthe tap of potentiometer 38is reduced so as to correspond to a new and lower warp strain that isrequiredfor sparing the warp when the loom is out of operation.Whenrestarting the loom by actuation of main switch 25, switch 35 isre-opened whereby the original value of reference voltage U isre-established and thus the warp tension is restored to the valuerequisite for weaving.

Looms are made in which a clutch is provided between drive motor 29 andmain shaft 20. For starting and stop ping the loom, said clutch isengaged and disengaged while the motor is running, with the aid of alever. In this case switch 35 is combined not with main switch 25 butwith the clutch-actuating lever. When the clutch is disengaged switch 35is closed, and is opened when the clutch is engaged.

Signal U passes through a compensator 30 which comprises a variableresistor 31 and a fixed resistor 33 as well as a variable capacitor 32.Compensator 30 serves for synchronizing the phase position of thedeviations of signal U with the oscillations of the loom parts, sincethe warp tension fluctuations appearing on whip roll 5 and contained insignal U have to agree with the tension peaks actually occurring whenweaving. Furthermore, with resistor 31 is variable the magnitude ofsignal U' delivered to an amplifier 40.

In the latter signal U is magnified to a value sufiicient to convert ingearing 10 the constant driving speed of wheel 13 into the requiredrotary movements of shaft 67 or, respectively, of warp beam 1. Amplifier40 is so gaged that, for positive signals U' for example, an outputsignal U' is given on to a pair of lines 151, 102 and that for negativeinput signals U the output signal U, is delivered to the pair of lines101, 103.

The amplifier 40 is energized by still other electrical pulses U' U"which pass via lines 104, 105 and 106 and vary the warp beam movementsas will be explained below.

FIG. 1a shows a possible wiring scheme for such an amplifier. Itcomprises in the main two separate amplifiers 401, 402 of which one, forexample amplifier 401, serves for signals U' that are negative withrespect to earth. Parallel to signal U furthermore, pulses U' U"controlled by the loom itself are delivered to the amplifiers 401, 402.For this purpose, lines starting from a voltage source 46 lead to theamplifier inputs via contact means 16, 17 and resistors 45, 167 and 198.

FIG. 2 shows another form of converter 9. Coil 42 here comprises ahousing made of magnetically conducting material that is provided withtwo symmetrical coil half portions 91, 92 on either side of a movablearmature 41'. The latter again is connected to the movable whip roll-5by reason of the fact that a spring 39 presses the rod which carriesarmature 41, against whip roll 5; and the armature thus follows themovements of roll 5. These variations in position produce in the twocoil half portions 91, 92 changes of the output voltages which areconverted into direct voltages U U in rectifiers 44, 47 and smoothed infilters 48, 49. These signals U U are subtracted from each other,whereby results a differential signal U A resistor 93 in series with aswitch 36 is parallel to the direct voltage U When switch 36' is closed,direct voltage U assumes another value than when it is open so that forthe purpose of compensation another Warp tension and, therefore, anotherdirect voltage U arises. Switch 36', FIG. 2, is cut in when the warptension is to be arbitrarily changed and thus may be a part of acombined tapping switch which further comprises a switch part 36",FIG. 1. A further switch 35 that serves for the same purpose as in theearlier paragraph and FIG. 1, is operated either together with mainswitch 25 or with the loom disengaging lever and establishes that warptension which is required for sparing the warp 2 when the loom is out ofoperation.

FIG. 3 shows the direct voltages U U and their difference U in functionof the displacement or stroke s that armature 41 may undergo under theinfluence of the movements of whip roll 5. Coil 92 of converter 9through rectifier 44' supplies the signal U which in function of strokes follows a parabola-like path, and signal U follows an opposite-path.Thereby the difference of the direct voltages at the point Where s=0 isalso zero. Thus there is always a definite value of signal U on theentire path from s to +s. When the position of armature 41' changes byan amount As for example, U increases by AU and U decreases by AU Theresult is a change of signal U by AU For the purpose of setting acertain warp tension, this type of converter 9 has to be mounteddisplaceably with respect to loom frame 27 and its position fixed, forexample, by means of a micrometer screw. While in the arrangement shownin FIG. 1 the electrical magnitude U may be tapped from a constantvoltage source 34, in converter 9 of FIG. 2 U as well as U are directlydependent on the position of armature 41'. Thus there are no othersetting means for changing a reference quantity than the position of thehousing of converter 9 relatively to loom frame 27.

FIG. 4 shows a characteristic of an amplifier 40 in which positive inputsignals +U effect a positive output signal U and negative input signals-U effect a negative output signal U For the present application it isnecessary, however, that for input signals having positive or negativepolarity the corresponding output signal appears on different lines, ashas already been called for earlier in the description of FIG. 1. Tosuch end the output voltages U; of FIG. 4, for example, could besubdivided into such separate signals U,,, U".; through a simplerectifier arrangement. In such case, a diagram as shown in FIG. 5 isobtained in which positive signals U' yield positive amplified signalsU.;, and in which negative signals -U' yield positive amplified signalsU" These signals are evaluated in gearing of FIG. 1 by converting aconstant speed of a drive wheel 13 into a movement of worm 4 and thus ofwarp beam 1, that is controlled by the signals U'.,, U".;. An embodimentof such a gearing 10 is shown in FIG. 6.

Drive is taken from motor 29 via wheel 13 on to a pinion 61 which mesheswith the spur gear 62 of a first differential gearing 60. To spur gear62 is fixed a cage 63 in which revolves a planetary gear 64 meshing withtwo bevel gears 65, 66. Bevel gear 65 is fast on shaft 67 that driveswarp beam 1 via worm wheel 3, worm 4 and bevel gearing 71, 72. The speedof shaft 67 is designated by n Bevel gear 66 through a shaft 68 isconnected to a spur gear 6? and rotates at a speed 11 While the speed 11of spur gear 62 is substantially constant, speed 11 of shaft 67 isvaried by a speed n communicated to shaft 68 via an intermediate gearing'70 comprising spur gears 59, 69. To such end, spur gear 52 of a seconddifferential gearing 50 also is driven at a constant speed 11 Spur gear52 carries a cage 53 with a planetary gear 54 that meshes with bevelgears 55, 56. Bevel gear 55 is fast on a shaft 58 on which spur gear 59also is fast. Shaft 58 on its other end carries the rotor 12 of anelectrically controllable brake 12. On the opposite side the rotor 11'of a second electrically controllable brake 11 is connected to bevelgear 56 by shaft 57. The speed of the latter is designated by 11 andthat of shaft 58 by In. The two brakes 11, 12 are excited by the signalsU.,, U".; supplied by amplifier 40 to thereby bias speed 11 of shaft 58.As speed 11 acts on the first differential gearing 60 via intermediategearing 7t certain speeds result for shaft 67, depending on themomentary state of excitation of the two brakes 11 and 12.

These speeds and directions of rotation are given in the followingtable, provided'that the speeds n ,n of the oppositely rotating gears62, 52 are equal and the speed 11 (shaft 68) is twice as high as that ofshaft 58, the shafts 58 and 68 rotating in opposite directions.

By only partly exciting the brakes 11 and 12, driven shaft 67 of thefirst differential gearing 60 may be rotated at any speed between +2nand -2n A ratio n zn of the gears 62 and 52, different from -1, may beem ployed, provided that the ratio n :n of intermediate gearing 70 ischanged likewise. This affords high-speed operation of the two rotors 11and 12 so that the shafts 57, 58 due to the small torque can be sloweddown to standstill by weak signals U This construction of gearing 16 incombination with the measurement of the warp tension P on theresiliently mounted whip roll 5 have made it possible to keep constantthe warp tension not only in the average for a plurality of weavingcycles but to also control same within a single weaving cycle. This hasbeen attained by reason of the fact that the parts of gearing 10 thatrotate at high speed are of small mass and thus can be accelerated anddecelerated in very short time. 7 FIG. 7 first shows the warp tension Pplotted against time t in combination with the position or stroke H ofthe weaving shafts. At point A shed 19 (FIG. 1) is closed, and the warptension thus is a minimum. When shed 19 is opened, up to point B,additional warp length is required as manifested by a rise in warpstrain. In the open-shed position B-C the warp tension also remains atits high value. In this interval a pick occurs, followed by thebeating-up movement which gives origin to a brief and extraordinarilyhigh warp tension peak. The following shedding change CD-E gives rise toa drop and renewed rise of the warp tension, while the open-shedposition E-F is combined with high Warp tension.

The subdivision of the weaving cycle into -time intervals as shown inFIG. 7, is a simplification. These time intervals are determined by themode of operation of the loom parts that move the weaving shafts 18, andthis mode of operation is determined by the requirements of fabricformation. The extent of the individual intervals with varying orconstant warp tension, however, are not critical for the mode of actionof the let-off.

In'order to supply additional warp length at the moment of shed openingand to stretch the warp at the proper time when closing the shed, thewarp beam revolutions requisite therefor are synchronized with theweaving cycle. This is readily possible since, as explained before, theelectrically controlled gearing reacts so rapidly to signals U',,, U".,that the warp tension fluctuations within a strain alternation can atleast be damped substantially, if not entirely compensated. When,however, the requisite warp beam movement is solely controlled by thewarp strain acting on the whip roll, said movement certainly is alwaystoo late since the warp demand has to manifest itself first by theformation of increased warp tension. The weaving cycle, however, affordsthe possibility to control the accurately predictable additional warplength or warp excess, respectively, by exciting the reversal of thewarp beam movement at the moment when the additional warp beam demand orexcess starts to become effective, while the amount of the requisitesupply or take up is adapted to the actual warp strain. To such end,pulses U' U" timed by the loom drive are delivered by contact means(FIG. 1) to amplifier 40, which pulses are contained in the amplifiedsignal U.,, U".; and initiate the requisite warp beam movements.

In the lower portion of FIG. 7 these pulses U' U";, are plotted againsttime t and in combination with the course of warp tension P. A firstpulse U leads, with respect to inoment C, by the angle to and initiatesa partial warp beam revolution that is necessary due to the warp straindrop in the interval CD. The magnitude of the warp strain is determinedby the signal U' as soon as pulse' U' is terminated. From this pulse U'and by an angle a later, a further pulse U" is delivered thatanticipates the imminent rise in the warp strain during the interval D-Eby preparing a warp beam rotation in 7 the sense of warp pay-out. Untilsuch reversal starts to become effective the moment D is attained atwhich the magnitude of the warp tension again is prescribed by signal U'The angles of lead (p and a as well as the pulse duration 1- depend onthe mode of operation of the loom and have to be ascertained bypractice.

In FIG. 1 the formation of the pulses U' U" is shown by a cam fast oneccentric shaft 14 and by contact means 16, 17. A source of potential 46supplies the pulse potential when the contact means 16, 17 are closedwhile the amplitude thereof may be set by means of a variable resistor45.

The interval of the pulses U' U" i.e. the angle a, is given by themutual position of the contact means 16, 17. Lead angle a is determinedby the position of cam 15 with respect to eccentric shaft 14. As thespeed of the latter is only half that of loom main shaft 20, there aretwo cams 15 provided, i.e., each pair of contact means 16, 17 is closedtwice during each revolution of shaft 14.

The ready and rapid control action of electrical signal U on warp beam 1further permits lowering the warp tension during loom standstill andraising it once when restarting to the original value required for theweaving operation, and this even before the first weft thread is forcedinto place against the fell of the cloth. Such rapid restoration of thewarp tension avoids the phenomenon feared so much in weaving, namely,that loom standstills become visible in the cloth by stripes that appearimmediately after restarting due to improper warp tension during a fewpicks or weft insertions. The quality of the cloth produced issubstantially improved thereby and losses due to impermissible stripeformation are avoided.

A further advantage of the electric control of the warp tension is thatthe warp also may be arbitrarily let off by simple means to any extentdesired and the operational warp tension nevertheless be automaticallyreestablished. To such end is provided a switch 36' (FIG. 2) which bycutting-in switch means changes the reference voltage U so far that evenin case of a slack warp 2 still such a signal U' remains that warp beam1 further lets off warp. Only when, by further actuation of switch 36,the switch part 36" interrupts the lines 101 to 103, the warp beam driveis stopped. For the purpose of retensioning the warp, switch 36 with itsparts 36', 36", only has to be restored to its initial positionwhereupon the proper warp tension is automatically re-established, asgiven by a certain position of whip roll 5 with respect to loom frame27.

It should be noted that the rotational movements of the warp beam 1,i.e. its angular movements, are relatively small because the warpconsumption per shuttle pick amounts to only a fraction of an inch (afew millimeters). Since there is enough driving power available, thenecessary mass forces can be made available without ditficulty. The fastrotating parts of the gear 10, particularly the rotors 11 and 12' of thebrakes 11 and 12, only distribute the transformed power and, therefore,do not transmit great torques so that the rotating masses may be heldsmall. Their inertia is small and they can be accelerated anddecelerated within very short periods of time. All this makes itpossible to effect the necessary warp beam movements in conventionallooms performing up to 200 picks per minute.

Iclaim:

1. In a method for maintaining the tension of the warp supplied from awarp beam in a loom, the steps of:

producing a first electric signal corresponding to the warp tension,

comparing said first signal with a second electric signal thatcorresponds to the set point of the warp tension for producing a thirdelectric signal that corresponds to the difference between the first twosignals and has a certain polarity when the warp tension exceeds the setpoint and has the opposite polarity when'the warp tension is below theset point,

amplifying said third signal to produce a fourth signal,

actuating an electromechanical motor operator including a shaft by saidfourth signal to change the rotation of the shaft upon a polarity changeof the third signal and to rotate the shaft at a speed corresponding tothe amplitude of the fourth signal,

rotating the warp beam at a direction and speed corresponding to thedirection and speed of the shaft whereby the warp beam pays out warp atincreasing warp tension and takes up warp at decreasing warp tension,

producing an additional electric signal of a certain polarity whenclosing the shed of the loom and producing an additional electric signalof the opposite polarity when opening the shed, and

amplifying said additional signals and superimposing same on the fourthsignal for operating said shaft and the warp beam to let off additionalwarp upon opening the shed and to take up warp upon closing the shed,independently of the magnitude of the third signal.

2. In a method for maintaining the tension of the warp supplied from awarp beam in a loom, the steps of: producing a first electric signalcorresponding to the warp tension,

comparing said first signal with a second electric signal thatcorresponds to the set point of the warp tension for producing a thirdelectric signal that corresponds to the difference between the first twosignals and has a certain polarity when the warp tension exceeds the setpoint and has the opposite polarity when the warp tension is below theset point,

amplifying said third signal'to produce a fourth signal,

actuating an electromechanical motor operator including a shaft by saidfourth signal to change the r0- tation of the shaft upon a polaritychange of the third signal and to rotate the shaft at a speedcorresponding to the amplitude of the fourth signal,

rotating the warp beam at a direction and speed corresponding to thedirection and speed of the shaft whereby the warp beam pays out warp atincreasing warp tension and takes up warp at decreasing warp tension,

automatically reducing the warp tension to a predetermined value uponstopping the loom, and automatically restoring the warp tension uponrestarting the loom and prior to the first weft insertion after thestandstill.

3. The method of maintaining substantially constant the tension of thewarp supplied to the sheds from the warp beam in a loom, which comprisesvarying the rate at which warp is supplied in synchronism with theweaving cycle of the loom to anticipate and minimize the changes intension due to the opening and closing of the sheds, measuring theactual variations in the Warp tension and further varying the rate atwhich the warp is supplied to compensate for the actual variations.

4. In a loom comprising a warp beam for letting off warp, weaving shaftsfor forming sheds of the warp paid out by the warp beam, and drive meansfor driving the warp beam and said shafts, the improvement comprising:

first means for measuring the warp tension after the warp has left thewarp beam,

second means connected to the first means to produce a first electricsignal corresponding to the tension of the warp,

a source of potential producing a second electric signal correspondingto the set point of the warp tension, 7

third means connected to the second means and to the source of potentialfor producing a third electric signal that corresponds to the diiferencebetween the first two signals and has a certain polarity when the warptension exceeds the set point and the opposite polarity when the warptension is below the set point,

an electric amplifier connected to the third means to receive andamplify the third signal for producing a fourth electric signal,

an electromechanical motor operator including a rotatable shaft andconnected to the amplifier to receive the fourth signal for reversingthe direction of rotation of the shaft upon a polarity change of thefourth signal and for controlling the speed of the shaft to correspondto the amplitude of the fourth signal,

said shaft being operatively connected to the warp beam for rotating thelatter in a direction and at a speed corresponding to the direction andspeed of the shaft,

means for stopping and starting the loom, and

means connected to these stopping and starting means a for setting saidsecond electric signal, upon stopping of the loom, to correspond to awarp tension below that required when the loom is in operation and forsetting said second electric signal, upon starting of the loom, tocorrespond to the set warp tension required for normal weaving.

5. In a loom comprising a warp beam for letting oif warp, weaving shaftsfor forming sheds of the warp paid out by the warp beam, and drive meansfor driving the warp beam and said shafts, the improvement comprising:

first means for measuring the warp tension after the warp has left thewarp beam,

second means connected to the first means to produce a first electricsignal corresponding to the tension of the warp,

a source of potential producing a second electric signal correspondingto the set point of the warp tension,

third means connected to the second means and to the source of potentialfor producing a third electric signal that corresponds to the differencebetween the first two signals and has a certain polarity when the warptension exceeds the set point and the opposite polarity when the warptension is below the set point,

an electric amplifier connected to the third means to receive andamplify the third signal for producing a fourth electric signal,

an electromechanical motor operator including a rotatable shaft andconnected to the amplifier to receive the fourth signal for reversingthe direction of rotation of the shaft upon a polarity change of thefourth signal and for controlling the speed of the shaft to correspondto the amplitude of the fourth signal,

said shaft being operatively connected to the warp beam for rotating thelatter in a direction and at a speed corresponding to the direction andspeed of the shaft,

means for modifying the timing of the operation of the warp beamindependently of said third signal, comprising:

two switches,

means operated by the 100111 drive means for periodically closing saidswitches for predetermined intervals, and

circuits including sources of potential connecting said switches to saidamplifier to transmit thereto pulses produced by the periodic closing ofthe switches for modifying the fourth signal controlling the rotatableshaft.

References Cited in the file of this patent UNITED STATES PATENTS2,032,176 Kovalsky Feb. 25, 1936 2,430,639 Jacques Nov. 11, 19472,843,882 Louis et al. July 22, 1958 2,871,685 Bassist Feb. 3, 19592,877,397 Poschner et a1 Mar. 10, 1959

1. IN A METHOD FOR MAINTAINING THE TENSION OF THE WARP SUPPLIED FROM AWARP BEAM IN A LOOM, THE STEPS OF: PRODUCING A FIRST ELECTRIC SIGNALCORRESPONDING TO THE WARP TENSION, COMPARING SAID FIRST SIGNAL WITH ASECOND ELECTRIC SIGNAL THAT CORRESPONDS TO THE SET POINT OF THE WARPTENSION FOR PRODUCING A THIRD ELECTRIC SIGNAL THAT CORRESPONDS TO THEDIFFERENCE BETWEEN THE FIRST TWO SIGNALS AND HAS A CERTAIN POLARITY WHENTHE WARP TENSION EXCEEDS THE SET POINT AND HAS THE OPPOSITE POLARITYWHEN THE WARP TENSION IS BELOW THE SET POINT. AMPLIFYING SAID THIRDSIGNAL TO PRODUCE A FOURTH SIGNAL, ACTUATING AN ELECTROMECHANICAL MOTOROPERATOR INCLUDING A SHAFT BY SAID FOURTH SIGNAL TO CHANGE THE ROTATIONOF THE SHAFT UPON A POLARITY CHANGE OF THE THIRD SIGNAL AND TO ROTATETHE SHAFT AT A SPEED CORRESPONDING TO THE AMPLITUDE OF THE FOURTHSIGNAL,